1. Field of the Invention
The present invention relates to a magnetoresistive element which detects magnetism by passing a sense current in a direction perpendicular to the plane of a magnetoresistive film, and a method of manufacturing the same.
2. Description of the Related Art
At present, magnetic recording apparatuses such as HDD (hard disk drive) are used in applications of personal computers, portable audio/video players, video cameras and car navigation system. A further increase in recording capacity of HDD is desired with the expansion of applications. For increasing recording capacity without increasing the volume of HDD, further improvement in recording density per unit area is needed.
The area of one bit recorded in a magnetic recording medium is decreased with improvement in recording density. As a result, a magnetic field signal from the recording medium becomes very weak to make a conventional read head difficult to distinguish between “0” and “1”. Accordingly, a read head having high magnetic field sensitivity is required with improvement in recording density.
The performance of magnetic devices, particularly magnetic heads, has been drastically improved by using the giant magnetoresistive effect (GMR) and tunneling magnetoresistive effect (TMR). Particularly, application of a spin-valve film (SV film) to magnetic heads and magnetic random access memories (MRAMs) has brought about marked technical improvement in the field of magnetic devices.
The “spin-valve film” is a stacked film called a spin-dependent scattering unit having a structure in which a nonmagnetic spacer layer is sandwiched between two ferromagnetic layers. In the spin-valve film, the magnetization of one ferromagnetic layer (referred to as a “pinned layer” or “magnetization pinned layer”) is pinned by an antiferromagnetic layer or the like, whereas the magnetization of the other ferromagnetic layer (referred to as a “free layer” or “magnetization free layer”) is made rotatable in accordance with an external magnetic field. In the spin-valve film, a giant magnetoresistace change can be produced by a change of the relative angle between the magnetization directions of the pinned layer and the free layer.
Magnetoresistive elements using the spin-valve film include CIP (current-in-plane)-GMR element, CPP (current-perpendicular-to-plane)-GMR element, and TMR (tunneling magnetoresistance) element. In the CIP-GMR element, a sense current is conducted in parallel to the plane of the spin-valve film, and in the CPP-GMR and TMR elements, a sense current is conducted in a direction substantially perpendicular to the plane of the spin-valve film. The trend of high recording density heads is toward the system of conducting a sense current perpendicularly to the plane.
Conventionally, there is known a magnetoresistive element comprising a magnetoresistive film including a pinned layer, a free layer, a spacer layer, and a thin film layer having an oxide, nitride or oxynitride formed in the pinned layer, in the free layer, in the interface between the pinned layer and the spacer layer, or in the interface between the free layer and the spacer layer, and a pair of electrodes that pass a sense current in a direction approximately perpendicular to the plane of the magnetoresistive film. See JP-A 2004-6589 (KOKAI). The thin film layer is permeable preferentially to either up-spin electrons or down-spin electrons, thus contributing to production of higher magnetoresistive ratio (MR ratio). Such thin film layer is called a spin filter layer (SF layer). Even if the SF layer is small in thickness, the SF layer can generate a difference between up-spin electron permeation and down-spin electron permeation and is thus advantageous to narrower head gap.
However, it came to be found that the conventional spin filter layer is insufficient in the difference between up-spin electron permeation and down-spin electron permeation and there is room to enable higher MR ratio.